Diesel combustion exhaust is a regulated emission. Diesel particulate matter (PM), is the particulate component of diesel exhaust, which includes diesel soot and aerosols such as ash particulates, metallic abrasion particles, sulfates, and silicates. When released into the atmosphere, PMs can take the form of individual particles or chain aggregates, with most in the invisible sub-micrometer range of 100 nanometers. Various technologies have been developed for identifying and filtering out exhaust PMs before the exhaust is released to the atmosphere.
As an example, PM sensors, also known as soot sensors, may be used in vehicles having internal combustion engines. A PM sensor may be located upstream and/or downstream of a diesel particulate filter (DPF), and may be used to sense PM loading on the filter and diagnose operation of the DPF. Typically, the PM sensor may sense a particulate matter or soot load based on a correlation between a measured change in electrical conductance (or current/resistance) between a pair of electrodes placed on a planar substrate surface of the sensor with the amount of PM deposited between the measuring electrodes. Specifically, the measured conductivity provides a measure of soot accumulation. As such, the PM sensor sensitivity may be affected by size of particulates accumulated on the measuring electrodes. For example, when a large particulate gets deposited between the measuring electrodes, a PM sensor current may quickly saturate, thereby reducing the sensitivity of the PM sensor to detect particulates depositing thereafter. In addition, large particulates deposited on the electrodes may lead to false indication of DPF degradation and unwarranted replacement of functioning filters. Furthermore, the distribution of the particulates on the PM sensor electrodes may also affect the current measured by the sensor, thus leading to errors in the output of the PM sensor. Herein, the PM sensor capturing the PMs exiting the DPF, may not truly reflect the DPF filtering capabilities.
One example PM sensor design is shown by Roth et al. in U.S. Pat. No. 8,823,401. Therein, a pair of planar adjacently placed interdigitated electrodes, connected to a common voltage source are used to independently detect PMs in the exhaust. As the PMs deposit on the interdigitated electrode pair due to electrostatic attraction between the charged PMs and the electrodes, the output of the two independent PM sensors are further analyzed and compared using extensive algorithms to derive meaningful information to distinguish larger particulates in the exhaust.
However, the inventors herein have recognized potential issues with such an approach. The PM sensors described by Roth et al. may continue to have issues with large particulates saturating the PM sensor current, and thereby affecting the PM sensor sensitivity. Additionally, the sensor output of Roth et al., requires analysis with extensive algorithms to derive meaningful information regarding PMs in the exhaust, leading to extended processing times and undesired delays in data output and diagnostics.
The inventors have identified an approach to partly address these issues while improving sensitivity of the PM sensors. In one example, the issues described above may be addressed by a method for adjusting engine operation responsive to a distribution of particulates on a plurality of electrode pairs positioned inside a common particulate matter (PM) sensor housing of a PM sensor. As such, each individual electrode pair of the plurality of electrode pairs may be connected to different voltage sources and current measured across each electrode pair may be summed to generate the total PM sensor current. As a result, PM accumulation across each individual electrode pair may be monitored independently, and particulate six distribution may be tabulated.
As one example, large particulates depositing on one of the electrode pairs may saturate the current measured across that particular electrode pair, while leaving the remaining electrode pairs unaffected. The technical effect of summing the current generated across the plurality of electrode pairs of the PM sensor to generate a total current of the PM sensor is that the total PM sensor current may not saturate and may continue to increase as PMs continue to get deposited on the remaining electrode pairs. In this way a more accurate measure of the exhaust PM load, and thereby the DPF PM load can be determined. As such, this improves the efficiency of filter regeneration operations, and reduces the need for extensive algorithms. In addition, by enabling more accurate diagnosis of an exhaust DPF, exhaust emissions compliance may be improved. As such, this reduces the high warranty costs of replacing functional particulate filters and exhaust emissions are improved and exhaust component life is extended.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.